Drum support for steam boiler



Nov. 12, 1968 K. s. SVENDSEN 3,410,253

DRUM SUPPORT FOR STEAM BOILER Filed Jan. 13, 1967 AGENT 3,410,253 DRUM SUPPORT FOR STEAM BOILER Konrad S. Svendsen, Bloomfield, Conn., assignor to Combustion Engineering, Inc Windsor, Conn., a corporation of Delaware Filed Jan. 13, 1967, Ser. No. 613,387 6 Claims. (Cl. 122-510) ABSTRACT OF THE DISCLOSURE A support structure for supporting an elongated cylindrical vessel by means of U-hangers at each end with the legs of the U-hangers having means for adjusting the length thereof with respect to a fixed support structure from which the vessel is suspended, and the vessel being subject to lateral thermal forces tending to move the ends with respect to the fixed support structure, thereby creating undesirable bending stresses in the legs of the U-hangers. To reduce these bending stresses a near-frictionless cylindrical bearing having a fixed axis of rotation is interposed betWeen the adjusting means and the support structure with the bearing surface of the bearing preferably being lined with a self-lubricating metal liner.

This invention relates to steam boilers which are suspended from overhead structural steel, and is more particularly concerned with supporting by means of drum hangers a portion of the boiler including the steam and water drum and the tubes connected thereto as well as other equipment attached to the tubes such as boiler casing.

In large modern steam generators operating at high pressures the temperature of the drum and tubes reaches a relatively high value. This results in substantial displacement of the drum due to thermal expansion of the drum and the tubes. Often the load carried by the drum hangers exceeds one million pounds. Since the pressure at which many modern steam generators are operating approaches the critical pressure of 3206 lb./sq. in., the temperature of the steam contained in the drum and the tubes may exceed 700 F. Thermal expansion of these boiler parts, therefore, often amounts to several inches. This displacement of the drum relative to the overhead supporting steel imposes a considerable bending stress on the hanger rods, in addition to the tensional stress due to load. Accordingly, hanger rods often exceeding 7 inches in diameter must be used to carry these loads. In large boilers generating more than one million pounds of steam per hour the overhead supporting steel may be at an elevation of 30-40 feet above the drum elevation. However, steel rods are not commercially available of the diameter and length required to make the drum hanger out of one piece. Accordingly, to fabricate the drum hanger, several pieces of steel rod must be joined by welding. Because of the large diameter this requires an expensive welding procedure. Furthermore, maintaining uniform temperatures during welding and cooling of these welds is difiicult. Ways and means must therefore be found, if possible, to ease the requirements which call for hanger rods of large diameter.

In boilers of moderate size and where the load carried by the drum hanger is not unusually high, excessive bending stresses in the hanger rod are avoided by suspending the drum hanger from rocker plates having a rounded bearing surface. However, measurements on actual installations have shown that the rocker plates are only about 50% effective in reducing the bending stress in the drum hanger. It was found, as the load increases that the bearing surface of the rocker digs into the surface of the underlying bearing plate, reducing and eventually preventing etfective roller action.

States Patent Another way to reduce bending stresses in hanger rods is to increase the length of the rods so as to provide more flexibility. This, however, requires the raising of the supporting steel, the lengthening of the supporting columns and the increasing of the height of the building, a very costly remedy.

It is accordingly an important object of the invention to provide a drum hanger supporting assembly in which the frictional resistance in the hanger supporting parts is materially reduced. This in turn has the effect of substan tially reducing the bending stress in the hanger rod which reduction permits the use of a smaller rod diameter and/ or a shorter hanger length combined with a reduction of the required height of the supporting steel. Substantial savings in material and fabrication costs of the hanger rods and in the supporting and building steel can thereby be realized.

Other objects and advantages of the invention will become apparent from the following description of an illustrative embodiment thereof when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a partial elevation cross section of a steel generator being suspended from overhead steel;

FIG. 2 is a plain view of the steel drum and supports and showing the directions in which the drum ends tend to move clue to thermal expansion;

FIG. 3 is a partial cross section and elevational vieW of the end of one U-hanger leg and the yoke assembly from which it is supported;

FIG. 4 is a cross section through the end of the U- hanger leg and the yoke when taken on line 4-4 of FIG. 3; and

FIG. 5 is a cross section through the yoke bearing when taken on line 55 of FIG. 3.

Referring now to the drawings wherein like reference characters are used throughout the designate like elements, the illustrative and preferred embodiment of the invention depicted therein includes a vapor generator designated generally as 10 and comprising a furnace chamber 12 lined with heat absorbing tubes 14 and in cluding roof tubes 16 which terminate in a steam and water drum 18. This drum is suspended from overhead steel 20 by means of drum hangers 22 engaging drum 18 at either end 24 as shown in FIG. 2. The steam generator is restrained by the surrounding steel work in such a manner that a fixed point 25 of zero horizontal expansion is maintained which point preferably is located approximately midway between front and rear of the boiler and at the centerline 26 thereof.

In a top supported steam generator such as that illustratively depicted in FIG. 1 a major portion of the vertical thermal expansion occurs downwardly from the center of drum 18. Thermal horizontal expansion of the tubes such as roof tubes 16 proceeds from point 25 toward drum 18 and thermal horizontal expansion of the drum proceeds from centerline 26 toward each end 24 of drum 18. The resultant direction of expansion for displacement of drum ends 24 accordingly takes place along lines 28 and away from point 25, the point of zero expansion as indicated in FIG. 2.

Referring again to FIG. 1, drum hanger 22 comprises a lower part 30 which takes a semi-circular shape adapted to cradle drum 18. One of a pair of straight rod lengths 32 extends from either end thereof to form the Ushaped drum hanger 22. Rod 32 is threaded at its upper end as shown in FIGS. 3 and 4 to receive nut 34 which rests on a beam or yoke 35. This beam in turn transfers the load onto a bearing member 36 attached to a base plate 37 and structural steel members 20.

In conventional designs the drum hanger is fabricated of round bar stock. The heavy loads imposed on these hangers call for diameters exceeding 7 inches, as earlier noted. Because the unusual length required cannot be procured commercially, one or more welded butt joints are therefore needed in the fabrication of the drum hanger. The large circular cross section of these welded connections make it especially difiicult and costly to produce a good weld. Furthermore, since quality control by X-raying of rods of large diameter is cumbersome and expensive, it is especially desirable as earlier herein stated to reduce the diameter of the hanger rods as much as possible while still maintaining required safety tolerances.

Also, as earlier pointed out, in conventional rocker designs the heavy loads carried by the drum hanger and imposed on the bearing plate cause some yielding of the metal of the rocker and the bearing plate which reduces the rocker effectiveness. Accordingly, large bending stresses are imposed on the hanger rod in addition to tensional stresses due to load. This together with the dithculties introduced in making the welded joints creates a problem of great concern to the boiler manufacturer.

In accordance with the invention these conditions have been considerably improved by changing the rolling action of the conventional hanger rocker to the sliding action of a bearing. Furthermore deformity of the bearing surface is avoided by distributing the load over a large area instead of concentrating it on a narrow contact strip, as is the case in the conventional rocker support. In addition, so as to still further reduce resistance to thermal expansion of the boiler structure, the bearing surface is lined with a self-lubricating metal such as, for example, that used in the bearing known in the trade as Lubrite bearing. The bearing metal of such a self-lubricating bearing may be bronze impregnated with graphite, or other substance such as molybdenum disulfide may be employed.

Thus in the preferred embodiment shown in FIGS. 3, 4 and 5 the beam or yoke 35 supporting each end of U- hanger legs 32 is provided at each end with an arcuate cavity faced with a self-lubricating bearing metal liner 38 of the type hereinabove described. This arcuate liner may be fastened to yoke 35 by pins 40 or other suitable means. The bearing member 36 having a complementary upper convex surface to match the concave surface of the liner 38 is supported on a bearing plate 44 resting on structural member 20. Obviously liner 38 could be attached to member 36 instead of yoke 35 with equally beneficial results. Each member 36 is positioned at a hanger such that its longitudinal axis is normal to the directions in which the drum ends 24 move, as indicated by lines 28 in FIG. 2.

In accordance with the invention therefore the drum hangers are provided with a supporting structure which employs sliding action in place of conventional rolling action, and in which bearings of the self-lubricating type are used. With such a support, when applied to the steam drums of large heavy boilers, considerable savings can be realized by virtue of a reduction in diameter and/or a reduction in length of the hanger rods.

For example, for a load of 368,000 pounds carried by each hanger rod and with a drum movement of 3 inches due to thermal expansion, a hanger rod of 7%. inches diameter and 40 feet length would be required when using the conventional rocker support.

On the other hand, if for the same load and expansion conditions a hanger rod supporting organization in accordance with the invention is employed, the length of the hanger rods can be reduced from 40 feet to 34 feet, 3 inches, while maintaining the same diameter. This permits not only a considerable saving in the cost of the hanger rod material but also in the structural support of the boiler and in the building steel and building walls.

Or, if it is desired to maintain the length of the hanger at 40 feet, the diameter of the rods can be reduced from 7 A inches to 6 inches. This reduction will not only represent a saving in material cost of the hanger but a substantial saving in welding costs can thereby be realized.

While I have illustrated and described a preferred embodiment of my invention, it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

I claim:

1. In a support structure for supporting an elongated cylindrical vessel and having a U-hanger including two upwardly extending legs for supporting said vessel; means associated with said vessel, which means when exposed to heat being subject to thermal forces tending to move said vessel in a direction which lies in the horizontal plane passing through the longitudinal axis of said vessel and which is at an acute angle with respect to said longitudinal axis; a fixed means of support spaced above said vessel from which supporting means said hanger and vessel is suspended, with said vessel tending to be displaced With respect to said fixed means of support; and adjustable means for limiting the effective length of said hanger legs; the improvement which comprises a cylindrical bearing having a fixed axis of rotation and being located below said adjustable means and between said adjustable means and said fixed means of support, said bearing comprising a lower separate semi-cylindrical part integral with said fixed support, and an upper separate semi-cylindrical part integral with said adjusting means, to permit rotational shifting of said upper part relative to said fixed lower part about said fixed axis of rotation; and a self-lubricating metal liner interposed between said first and said second part with said liner being fastened to one of said first and second parts.

2. The structure as defined in claim 1, wherein said lower part has an upper surface of convex shape and said upper part has a lower surface of concave shape.

3. The structure as defined in claim 2, wherein said liner is fastened to said upper part.

4. The structure as defined in claim 1, wherein said liner comprises a metal impregnated with graphite.

5. The structure as defined in claim 1, wherein said liner comprises a metal impregnated with molybdenum disulfide.

6. The method of supporting an elongated cylindrical vessel from an overhead fixed supporting structure with said vessel being subject to thermal forces tending to move said vessel with respect to said structure in a direction which lies in the horizontal plane passing through the longitudinal axis of said vessel and is at an acute angle with respect to said axis, comprising the steps of (a) suspending said vessel from said structure by means of U-hangers including upwardly extending legs having adjustable means;

(b) adjusting said legs by means of said adjustable means for limiting the elfective length thereof;

the improvement comprising the additional steps of:

(c) providing a rotational sliding motion about a fixed axis of rotation of said adjustable means with respect to said fixed supporting structure; and

(d) interposing a self-lubricating metal liner between said adjustable means and said support structure at the surface of mutual contact to reduce the bending stresses in the legs of said U-hangers.

References Cited UNITED STATES PATENTS 652,075 6/1900 Black 122-510 3,204,613 9/ 1965 Smith 1225 10 3,263,656 8/1966 Kurek.

KENNETH. W. SPRAGUE, Primary [.'.\'(llliirtul'. 

